Filled, two-part plastic-producing systems have assumed a position of major commercial importance. These systems are utilized throughout industry in applications ranging from the production of small molded articles, road surface coatings, and grouting (or mine bolt) for support of mine roof. The two parts of these systems are often packaged together to facilitate their use as, for example, a plastic or cement grouting. A representative embodiment of a cement grouting is described in U.S. Pat. No. 4,096,944 of Robert E. Simpson, the disclosure of which is incorporated herein by reference. Various plastic or hardening resin systems are also described in U.S. Pat. No. 4,096,944.
The first of the two basic parts of the plastic-producing systems comprises the combination of an unsaturated polyester resin and a vinyl monomer cross-linking agent. Ordinarily, these ingredients are combined in a weight ratio of between 9:1 to 1:4, still more usually 3:1 to 2:1, of resin to monomer to optimize cross-linking.
Suitable unsaturated polyester resins are well known. They have commonly been prepared by condensation of unsaturated polycarboxylic acids such as maleic, fumeric, aconitic and the like (or, if available, the corresponding anhydrides) with polyhydric alcohols such as ethylene glycol, butanediol and the like.
The vinyl monomers are likewise well known. Any compound contaning a polymerizable ##STR1## group may be employed. Representative preferred examples are compounds having a boiling point of at least 60.degree. C., such as styrene.
The second basic part of this system comprises a curing agent. Such agents, which initiate the cross-linking reaction between resin and vinyl monomer, are also well known. They include all types of free radical generators. Most commonly, however, benzoyl peroxide is employed because of its accepted advantages. While benzoyl peroxide alone may be employed, it is usually present in the form of a paste prepared by admixture with a liquid carrier such as a plasticizer or other diluent. This greatly increases the performance of the peroxide in initiating curing of the resin.
In addition to the already described ingredients of the present two-part systems, there is the filler. This essential ingredient may be present in either or both of these separate parts. It may be composed of any essentially inert, solid substance including, for example, clay, talc, wood flour and limestone. The filler generally constitutes between about 10% and 200%, more usually 50% and 160%, by weight of the first (resin plus vinyl monomer) part of the system. It is incorporated to supply both bulk and strength to the ultimate, cured resin or plastic product.
These two-part systems may, in addition to the foregoing, contain any of a large number of well known optional additives. These additives are useful in improving such systems or their products and include, merely by way of example, lubricants, resin rheology adjusters, pigments and the like.
While the conditions necessary for cure of resin in such systems may vary widely, the ingredients of the two parts are ordinarily and conventionally selected to provide for rapid cross-linking under ambient temperature. More specifically, the systems are designed to effect essentially complete curing within about 15 minutes at 30.degree. C. or less. This allows the two parts to be admixed, often in situ, and the cured or cross-linked plastic product then promptly produced without need for adjustment of reaction conditions.
Despite the well known and commercial nature of these filled, two-part plastic-producing systems, various drawbacks to their usage remain. This is particularly true where specialized applications are concerned. A recurrent problem of those systems relates to the use of benzoyl peroxide pastes. Such pastes tend to deteriorate and aften have a minimal shelf life. This obviously limits the manner in which they may be used.
A related drawback involves limits on effective activity. It has frequently been the case with these two-part plastic systems that separations of individual ingredients and/or mechanical limitations on admixture result in less than efficient utilization of benzoyl peroxide and/or lack of homogeneous products. This leads to increased cost and the potential for structural weaknesses.
Yet another drawback exists where it is sought to achieve castings of molded products. These two-part systems generally undergo significant shrinkage upon curing under ambient conditions. In addition, they have generally required the use of expensive metal molds where higher temperatures were utilized. As a consequence, they have not achieved optimum usage.
In the prior art two-part grout-producing system, as for example the cement system disclosed in U.S. Pat. No. 4,096,944 to Simpson, hydraulic cement is encased in a two-part rupturable bag with microencapsulated water. The resulting package, by virtue of the use of microencapsulated water, is expensive, and the encapsulating shells may not be completely impervious to water.
Despite the levels of use already achieved by filled, two-part plastic and grout producing systems, the foregoing and other drawbacks have exerted severe commercial limitations. It is therefore an object of this invention to minimize and/or overcome these and other problems as are discussed below.